The present invention relates to an insufflation apparatus improving the accuracy, safety and speed of insufflation of fluid into a human or animal body. Particularly, the invention relates to an apparatus adapted to regulate the pressure inside a body cavity by controllably increasing an interruption phase of an insufflation pulse upon identifying obstructions encountered by a Veress needle during and after its penetration into the body cavity.
Surgical procedures require the insufflation of fluid into a body cavity. Known insufflation apparatuses pass a fluid from the pressurized reservoir through the fluid line and an insufflation or Veress needle into the body cavity required to be maintained at a certain pressure.
The pressure to be regulated is the pressure of the patient, however, the pressure sensors are found inside the apparatus and measure the insufflation pressure upstream of an insufflation needle penetrating a patient""s body. Both pressures are only equal if no gas is flowing through the needle. This is the reason that electronic insufflators do not fill the operation area continually, but only in phases. A combination of a filling phase and an interruption phase during which the gas flow is constantly brought back to zero in order to measure the pressure of the patient constitutes a pulse.
U.S. Pat. No. 4,048,992 to Lindemann et al., discloses a pressure gauge reading a back pressure of insufflated gas built up with the predetermined insufflated gas volume upstream of a Veress needle. As time passes, the pressure differential across the needle becomes equal to zero as indicated by a zero flow rate on a flow gauge, thus making a user assume that the pressure inside a cavity is equal to the back pressure.
U.S. Pat. No. 4,676,774 to Semm et al., discloses an apparatus for the insufflation of gas into a body cavity and including a pressure gauge, whose measured value is fed as a function of time into an electronic evaluation circuit and is converted into the intraabdominal pressure. Such measurement is based on the experience that shortly after the start of insufflation, steady-state conditions occur so that the measured value of the pressure gauge is approximately constant. Since the measured value of the pressure gauge is time differentiated, the first derivative is equal to zero and corresponds to the insignificant intraabdominal overpressure built up in the cavity. Thus, the pressure on the pressure gauge upstream of the insufflator indicates the insufflator""s flow resistance and is constant. In order to calculate the static intraabdominal pressure the pressure at the start of insufflation has to be subtracted from the measured rising pressure.
U.S. Pat. No. 4,715,372 to Philippbar et al., discloses a gas insufflation apparatus for use in an arthroscopic attachment for a laser system in order to distend a joint during arthroscopic surgery. The apparatus includes a first regulator insufflating the gas directly into the knee joint at a minimal pressure and a second regulator applying the gas at a maximum pressure into an arthroscopic attachment.
U.S. Pat. No. 5,006,109 to Douglas et al., teaches a system for administering gas to a patient during an endoscopic procedure. The system includes a pressure regulator and a volumetric gas flow regulator continuously reflecting the pressure and flow rate of the gas which allow the user to modify these parameters during the procedure.
U.S. Pat. No. 5,360,396 to Chan discloses an apparatus for insufflation of a body cavity including a pressure reliever that allows the insufflating gas to escape if the pressure at the exit of a pressure reducer exceeds a predetermined pressure.
U.S. Pat. No. 5,439,441 discloses an insufflation device having a regulating device that is programmed to process and to store pressure reading values in the body cavity during each pause phase at which the introduction of gas into a body cavity to be inflated is discontinued. These readings are taken at plural, discrete intervals of time. The difference between a predetermined number of the most recent pressure reading values are compared to determined the pressure differential between highest and lowest pressure reading values. A series of results indicating that this pressure differential is less than a predetermined value determines that the pressure in the body has stabilized and equal to the pressure upstream of a needle inserted in the cavity.
U.S. Pat. No. 4,874,362 to Weist discloses a device and method for continuous insufflation wherein the intra-abdominal pressure is measured at an end of each cycle when a flow rate of gas is indicated to be zero. The rate is brought down to this value by controlling a pressure reducer that electrically connected with a CPU and whose working mode is a function of a clock generator and a nominal pressure generator. Particularly, the pressure reducer valve operates in two different modes. The first mode is characterized by maintaining a nominal pressure if a flow rate does not exceed a preset value. The pressure reducer is switched to the second mode, wherein an output pressure of the reducer is increased to a maximum insufflation value if the flow rate exceeds the preset value. The device disclosed in this reference operates without taking into consideration certain factors negatively affecting measurements of the intraabdominal pressure, for example, presence of gas flow through a Veress needle while a flow rate gage clearly indicates its absence.
All of the above disclosed devices are based on the premise that when an internal apparatus gas flow is brought back to zero at the end of a filling phase, no gas flows through a Veress needle into a body cavity thereby allowing correct determination of the intracavity pressure. During a surgical insufflation procedure of FIG. 1, an insufflation pressure Pins is shown to decay through a Veress needle in a relatively abrupt manner upon terminating a filling phase. Upon indicating a zero flow rate upstream of the Veress needle by a flow rate gauge, an equalization state between the insufflation pressure and an intracavity pressure Pabd is presumed to be reached and the intracavity pressure is measured within the interruption phase Ti=Tcxe2x88x92Tp of the pulse.
However, in many instances gas still flows through the Veress needle upon the presumed balance between the insufflation and intracavity pressures, thereby rendering the result of determination to be erroneous, as shown in dash lines in FIG. 1. The rational behind this phenomenon is the accumulation of gas at the upstream end of the Veress needle during a filling phase.
Typically, this is a result of obstructions encountered by the Veress needle during a surgery. For instance, during the pneumo-peritoneum penetration the needle may encounter the skin, the intra-abdominal wall, muscles. Each of these parts of a body adds to the dead volume of fluid that may eventually render the measurement of intracavity pressure dangerously low compared to an actual value.
Further, a modern high flow insufflator is capable of producing a gas flow rate up to 30 l/min that might be necessary in some surgical procedures at a phase when the intracavity pressure has stabilized. Many practitioners, knowing a desirable rate of gas flow, set a high target value at the start of insufflation. However, since the opening of the Veress needle allows only a low gas flow, usually not exceeding 2-2.5 l/min, the dead volume in front of the Veress needle is xe2x80x9cfilledxe2x80x9d with the maximum insufflation pressure. On completion of the filler phase, if the apparatus reduces the gas flow back to zero in order to measure the intracavity pressure, then there is still a pressure differential between the upstream and downstream ends of the needle. This dead volume decays through the needle into the cavity. Thus, although an internal apparatus gas flow is equal to zero, in fact gas flows from the dead volume in to the patient making measurements of the intracavity pressure erroneous.
Those flow conditions in the interior of the body in the immediate vicinity of the Veress needle are different during each insertion and further contribute to the inaccuracy of these measurements. Moreover, the complete line system including pressure reduces, moisturizes, heaters, and so on, differs between the individual operations thereby adding to the margin of error of the indicated pressure value.
Thus, safety considerations necessitate a need for an insufflation apparatus and method for administering a pressurized fluid to a body cavity which provides accurate determination and control of the intracavity pressure during an interruption phase between pulses when there is no undetected gas flow through a Veress needle.
The foregoing problems are solved by an inventive insufflation apparatus, wherein an accurate measurement of intracavity pressure is achieved by increasing an interruption phase of an insufflation cycle upon detecting obstructions that may successively be encountered by a Veress needle and a trocar in a body cavity. As a consequence of an increased interruption phase, a volume of pressurized fluid accumulated at an upstream end of the Veress needle dissipates through the Veress needle before measuring the intracavity pressure. Thus, a pressure regulator is controllable as a function of detecting an obstruction and a nominal pressure generator.
The inventive insufflation apparatus having two modes of operation available during a filling phase achieves this. In the first mode, the internal apparatus pressure is adjusted toward a minimum target value, which is generally equal to a preset nominal pressure, if both, a measure flow rate and a measured pressure are at most equal to predetermined values. However, once an obstruction encountered by the Veress needle manifests itself by an abrupt pressure increase and by an abrupt flow rate drop, a control processing unit (CPU) electrically switches the pressure controller to the second mode. Particularly, the controller""s output pressure defining an internal apparatus pressure is raised to its maximum (50 mmHg) for at least one insufflation cycle which is characterized by the increased interruption phase in accordance with this invention.
According to one aspect of the invention, the pressure controller is automatically switched to its second mode thereby increasing both, the internal apparatus pressure and, as a consequence, the dead volume upstream from the Veress needles. While the increased pressure helps overcome an obstruction, the dead volume needs an additional decay period of time that is automatically monitored by the CPU by controllably increasing the interruption phase and, as a consequence, the entire cycle. At the end of the interruption phase, the pressure gage correctly indicates an intracavity or intra-abdominal pressure. If, however, the obstruction persists, the next cycle is performed in accordance to the second mode of operation. Since this process is continuous, once the obstruction is overcome, the controller returns to its first normal mode of operation, so as the entire duration of the insufflation process is not significantly increased.
According to another aspect of the invention, in the first mode, the internal apparatus pressure is adjusted toward a minimum target value during the entire duration of a filling phase. However, if an obstruction encountered by the Veress needle is detected, the CPU of the insufflation apparatus is programmed to switch it to the second mode, wherein the internal apparatus pressure is increased to and maintained at a maximum value during only a portion of the filling phase. If the obstruction has not been yet passed through, then, upon termination of this portion of the filling phase, the controller interrupts the supply of pressurized fluid in the apparatus, thereby extending the interruption phase of pulse relative to the same interruption phase during the first mode. Thus, despite the fact that the dead volume in the second mode is greater than it is in the first mode, the duration of the interruption phase during the second mode is sufficient to allow the dead volume to empty itself before a measurement of an intracavity pressure is taken. However, according to this aspect of the invention, the cycle is not increased, and the entire duration of insufflation remains unchanged.
The insufflation apparatus according to the invention includes a gas supply system which has a pressurized gas storage reservoir, a pressure reduction valve, pressure and flow rate transducers coupled to the CPU, and a relief valve all connected to the gas supply line. An electronically operated pressure-regulating valve controllably blocking gas flow through the apparatus is responsive to the CPU for adjusting the pressure of fluid in the line within a 0-50 mmHg range. A cut-off electronically operated, which is in flow communication with the pressure-regulating valve, controllably switches the entire apparatus off upon expiration of the pre-set period.
In contrast to a typical feedback control that tends to bring a controlled value to the same preliminarily set target value, the method, in accordance with the invention, includes a step of setting a maximum target value at the time of detecting an obstruction. This is achieved, as previously described, by increasing the output signal of the electronic controller operating the pressure-regulated valve.
Upon detecting reestablishment of normal conditions, the insufflation apparatus returns to the first mode. Therefore, the apparatus and method in accordance with the invention provide an average gas flow during the entire duration of a surgical procedure and maintain substantially constant intracavity pressure regardless of obstructions encountered by the needle after the start of this procedure.
According to still another aspect of the invention, when the intracavity pressure has reached a nominal value, the Veress needle is replaced by a trocar having a large cross-section that allows the insufflator to operate at high flow rates. During this stage of operation, the most dangerous situation occurs when a leak is formed. Such leak may be, for example, a result of a faulty valve. Absent detection of the obstruction, a flow rate transducer visually indicates that a gas flow exceeds a preset flow rate, which automatically switches the apparatus in a third mode of operation monitored by the CPU. In contrast to the second mode of operation, this mode, while performed at an increased insufflation pressure, is characterized by a regular interruption phase, which is equal to the interruption phase of the first mode.
It is therefore an object of the invention to provide an insufflation apparatus maintaining safe administration of gas to a body cavity during an endoscopic procedure.
Another object of the invention is to provide an insufflation apparatus capable of monitoring precipitous variations in an internal apparatus gas flow and pressure signifying encounter of an obstruction by a Veress needle during its penetration into a body cavity.
A further object of the invention is to provide an insufflation apparatus adjusting its pressure in response to a precipitous variation in a measured intra-cavity pressure between nominal and maximum target values corresponding to first and second modes of operation of the insufflation apparatus.
Still another object of the invention is to provide an insufflation apparatus having an electronic controller automatically increasing both, an internal apparatus pressure and an interruption phase of the insufflation cycle.
A further object of the invention is to provide an insufflation apparatus controllably increasing an interruption phase and, as a consequence the entire duration of the cycle in response to detecting an obstruction.
Still another object of the invention is to provide an insufflation apparatus controllably increasing an interruption phase while decreasing a filling phase of the cycle so as to keep the total time of the cycle unchanged in response to detecting an obstruction.
Yet another object of the invention is to provide an insufflation apparatus having an electronic controller automatically adjusting an insufflation pressure in response to a precipitous increase in the measured gas flow above a preset flow rate.
Another object of the invention is to provide an electronic controller automatically determining duration of a filling phase and selectively switching the insufflation apparatus to a mode characterized by a maximum target value that is set in response to detecting obstructions encountered by a Veress needle.
A further object of the invention is to provide an insulation apparatus controllably increasing an internal apparatus pressure in response to a signal generated by a flow rate transducer that indicates a critical increase of the gas flow.
Still another object of the invention is to provide a method for measuring intracavity pressure, avoiding the inaccuracy of measuring during an endoscopic procedure.
Yet another object of the invention is to provide a method for measuring intracavity pressure in a pulsed manner and capable of detecting obstructions encountered by a Veress needle during penetration into a body cavity.
Another object of the invention is to provide a method for measuring intracavity pressure having two modes of operations characterized by different target values that are set in response to detection of obstructions encountered by a Veress needle.
Still another object of the invention is to provide a method for measuring intracavity pressure providing long decay periods for draining the dead volume of accumulated pressurized fluid without a perceptible reduction of the average gas flow.
While the following is shown and considered to be the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention.